Winch control system for constant load depth

ABSTRACT

A winch control system for operating a winch stationed on a vessel, and for stabilizing a load, which is connected by a cable to a traction unit driven by a prime mover, at a constant height above the sea floor irrespective of the vertical motion of the vessel due to wave action, thereby controlling the motion of the cable. A cable dynamics sensor, connectable to the cable between the traction unit and the load, generates output signals proportional (1) to its depth, and (2) to its velocity relative to the vessel. A tachometer, connectable to the traction unit, produces a signal which is proportional to the velocity of the cable relative to the vessel. A depth-velocity summing circuit, connected to the cable dynamics sensor, is adapted to be connected to a sensor depth order signal, generated by a control console on the vessel, for summing the sensor depth and depth order signals, and is connected to the cable dynamics sensor and tachometer for summing the sensor velocity signal and the cable velocity signal. The two depth and two velocity signals, after being summed, produce an output control signal. A torque control, adapted to be connected from the output of the depth-velocity summing circuit to the prime mover, develops a torque signal proportional to the control signal, to cause the traction unit to null the control signal, thereby controlling the load position and velocity.

United States Patent [72] inventors John M. McCool Altndeul;

Shelby F. Sullivan, Arcadia; Robert H. Hearn, Altadem; Michael S. Ball,

Pasadena, all 01, Call. [211 App]. No. 882,984 [22] Filed Dec. 8, 1969[45] Patented July 27, 1971 [73] Assignee The United States of Americaas represented by the Secretary of the Navy [54] WINCH CONTROL SYSTEMFOR CONSTANT LOAD DEP'I'H 7 Claims, 5 Drawing Figs.

[52] US. Cl 235/151, 114/235 B, 254/173 R [51] Int. Cl. 606; 7/78 [50]Field 01 Search 235/1502, 151, 151.32;340/29,177; 115/6, 6.1; 114/2352;254/173 R, 173 B [56] References Cited UNITED STATES PATENTS 2,729,9101/1956 Fryklund 114/2352 X 2,829,329 4/1958 Silva 235/151 X 3,351,89511/1967 Cupp et a1. 114/2352 X 3,469,821 9/1969 Gross et a]. 114/2352 XPrimary ExaminerMalcolm A. Morrison Assistant Examiner-Jerry SmithAllorneys- Richard S. Sciascia, Ervin F. Johnston and John StanABSTRACT: A winch control system for operating a winch stationed on avessel, and for stabilizing a load, which is connected by a cable to atraction unit driven by a prime mover, at a constant height above thesea floor irrespective of the vertical motion of the vessel due to waveaction, thereby controlling the motion of the cable. A cable dynamicssensor, connectable to the cable between the traction unit and the load,generates output signals proportional l) to its depth, and (2) to itsvelocity relative to the vessel. A tachometer, connectable to thetraction unit, produces a signal which is proportional to the velocityof the cable relative to the vessel. A depth-velocity summing circuit,connected to the cable dynamics sensor, is adapted to be connected to asensor depth order signal, generated by a control console on the vessel,for summing the sensor depth and depth order signals, and is connectedto the cable dynamics sensor and tachometer for summing the sensorvelocity signal and the cable velocity signal. The two depth and twovelocity signals, after being summed, produce an output control signal.A torque control, adapted to be connected from the output of thedepth-velocity summing circuit to the prime mover, develops a torquesignal proportional to the control signal, to cause the traction unit tonull the control signal, thereby controlling the load position andvelocity.

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INVENTORS SHELBY F. SULLIVAN ROBERT H. HEARN Ervin F Johnston ATTORNEYJohn Stan AGENT PATENTED JUL27I9YI 3 595 070 v SHEET 3 0F 3 48 ""1 lOUTPUT l STROKE HYDRAULIC CONTROL 67 SERVO VALVE CYLINDER I MOTOR SIGNALI 2 I I "0 GPM 2 63 FT-LB S2 2{w S+w 5 i l I 62 I Q94 I FEEDBACKTRANSFORMER MA (ERROR) l K I 60 i 66/ i .95. EE "T fi' OUTPUT CONTROLSIGNAL.

1 i 72 LOAD HIGH- LOW f BRAKES TORQUE 71/ ca LL CABLE THRESHOLD CONTROLTENSION CABLE-TENSION L MONITORING SYSTEM 49A 5/ 24 22 HYDRAULIC GEAR 7/MOTOR sox CAPSTANS g2 To CABLE DYNAMICS SENSOR INVENTORS F, G 5 JOHN M.MCCOOL SHELBY F SULLIVAN ROBERT H. HEARN MICHAEL 5. BALL Ervin FJohnston ATTORNEY ENT WINCH CONTROL SYSTEM FOR CONSTANT LOAD DEPTHSTATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

This invention relates to a winch control system, stationed on a vessel,for maintaining a load, connected by a cable to the winch controlsystem, at a constant depth below the mean sea surface, irrespective ofthe vertical motion of the ship due to wave action. It is not known ifthere are any systems of this type in the prior art.

This invention relates to a winch control system to hold a load at anearly constant depth below the mean sea surface compensating for theship's motion with cable motion. The implementation of the winch controlsystem for achieving this load positioning constitutes the invention.

This winch control system implementation is as follows:

The prime cable mover is a variable-stroke hydraulic motor, which drivesa pair of capstans and is fed from a constant pressure source, resultingin a device with torque on the capstans proportional to the stroke. Thetorque in turn is determined by the magnitude of the electrical signalfed to a torque control from a summing amplifier, herein termed adepth-velocity summing circuit.

The summing amplifier takes together all inputs from the system sensorsto create an error signal which drives the capstan to null the error,and hence control the load position and velocity.

The sensors and the signals they provide for system control are thefollowing:

1. The rate or velocity at which the cable wound around the capstansmoves is measured by a tachometer, and an electrical signal proportionalto this rate is fed into the summing amplifier. This signal representsthe rate of cable motion relative to the ship.

2. The cable dynamics sensor is a package rigidly attached to the cable,at a depth approximately 300 feet below the mean surface of the ocean.This depth is a compromise between being deep enough so that the effectof passing waves does not significantly alter the pressure (depth)readings at the sensor, yet shallow enough so that the mechanical delayof cable motion between the capstan and the sensor is not great enoughto cause system instability problems. There are two outputs from thesensor package, one proportional to the depth of the sensor, and oneproportional to the acceleration of the sensor, the latter beingintegrated to produce a velocity signal.

3. A constant signal from a control console, proportional to the nominaldepth at which the sensor package is to operate.

It is the choice and combination of these signals which allow the systemto operate successfully. Of particular importance was the choice of theacceleration term in the sensor package.

A stability analysis of the winch control system indicated that a signalproportional to the rate at which the cable dynamics sensor, and hencethe cable, was moving vertically was critical to achieving stability inthe system. The first attempt at providing this signal was throughelectronic differentiation of the depth signal. This resulted in asignal too corrupted with noise to be useful in the system. Sincedifferentiation is inherently a noiseincreasing process, amplifyinghigher frequency signals with respect to lower frequency signals, thiswas not surprising.

The alternative was to measure the acceleration of the sensor directly,and integrate this signal electronically once to provide a rate signal.This resulted in a relatively noise-free signal which was quite usable.There was no way found to measure the rate of the sensor directly, sinceall known devices for this job have time-lags between the time theystart moving and the time the signal actually represents the velocity.

In operation, then, the system functions in this manner:

a. The load is deployed and the cable dynamics sensor package taken tonear its desired depth.

b. A control order, or depth order, signal is set into the system fromthe console for the desired nominal position or depth of the sensor.

c. The system is turned into a constant depth mode of control, where thesensor outputs cause capstan motion.

In this mode, if the sensor is too deep relative to the order signal, bysay 10 feet, there will be an error signal at the output of the summingamplifier corresponding to the 10-foot error, which will cause thecapstan to rotate in a direction which will cause it to take in cable.The capstan will come to speed until the capstan rate signal is justsufficient to balance the combination of the depth error signal and thesensor rate, bringing the sensor to the correct depth at a controlledspeed, the speed being greater as the error in depth of the sensor isgreater. As the sensor achieves the correct depth, the capstan willslow, and finally stop when the sensor is correctly positioned.

Should the vessel rise up on a wave, the sensor outputs will indicateboth the change in sensor depth with respect to the means sea surface,and the rate at which it is changing. The summing amplifier output willcause the capstan to rotate in a direction to let cable out at the rateneeded to return the sensor to its nominal depth and zero velocity. Dueto the finite gain of the servo loop, there will always be some smallerror in the sensor position and it may have some motion. With the gainsimplemented and tested in the system, the sensor position error would beheld to within less than 1 foot, and its velocity to within much lessthan 1 foot per second with the ship riding a state 6 sea (shipexcursions about :6-8 feet, or 12-16 feet peak-to-peak amplitude).

For a vessel riding the trough of the wave, the results would he thesame, with changes in direction.

The cable tension was monitored as a safety feature,.and brakes takeeffect in the system if the tension goes too high or low. This brakingapparatus is not essential to the winch control system.

Accordingly, an object of the invention is the provision of a controlsystem for a winch which is capable of maintaining a load at a constantdepth below the mean surface of the ocean.

Another object is to provide a winch control system compensating forboth the displacement of the load and the rate of displacement, orvelocity, of the load.

A further object of the invention is the provision of a winch controlsystem which is substantially noise-free.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description, when considered inconnection with the accompanying drawings, in which like referencenumerals designate like parts throughout the figures thereof andwherein:

FIG. 1 is a pictorial view of the complete winch, with a sensor packageas a key part of the winch control system.

FIG. 2 is a cross-sectional diagrammatic view of a pressure source, inthe form of a fluid accumulator, for a cable accumulator, both beingimportant elements of the winch system.

FIG. 3 is a circuit diagram of the major servo loop of the winch controlsystem.

FIG. 4 is a circuit diagram of a minor servo loop around the motor usedas a prime mover.

FIG. 5 shows an optional braking arrangement to ensure that the cabletension is maintained within safe operating limits.

Before discussing the figures in detail, a few of the features of thewinch, of which the winch control system is a part, will be enumerated.

The winch has the following significant design features:

a. The cable is controlled at all points in the system to avoid bothslacking and overtensioning, with tension control and use of a cableaccumulator.

b. The winch is hydraulically powered with proportional torque controlthrough variable displacement hydraulic motors operating from aconstant-pressure source.

c. The hydraulic energy is controlled with high-band-width, closed loopcomponents. Care was taken to keep the system as linear and controllableas possible.

d. The winch is designed to compensate for ships motion by paying cablein and out as the ship falls and rises. This maintains the load at asubstantially constant depth below the mean sea surface.

e. The hydraulic system can store significant amounts of energy atpoints where high-peak power may be demanded. This reduces transientpower loads on the ship's electrical generators, and improves systemresponse.

f. Energy is dissipated directly by cooling heated oil at a lowpressure.

g. Complete control of the winch is carried out from a remote console,located on a vessel.

Referring now to the drawings, wherein like reference numerals designatelike or corresponding parts throughout the several views, there is shownin FIG. 1 a winch system 10, which onsists of five units: the tractionunit 12, cable accumulator 14, storage drum 16, hydraulic power supply18, and the control console 20. A sensor package 21, a key element ofthe invention, will be described more fully in connection with FIG. 3.

The traction unit 12 basically consists of a pair of capstans 24 groovedto take five wraps of cable 22. It is driven through a gear reductionbox (See FIG. 5) by a 150 hp. hydraulic motor with proportional torquecontrol. This unit is the working" unit in the system, developing thetorque required to hold and accelerate the load 23.

Maximum line tension is 8,000 lbs.; maximum line rate is 25 ft./sec.knots); maximum acceleration (no load) is 250 ft./sec. and minimum loadposition increment is less than one-half inch at full load.

The cable accumulator 14 is a passive cable storage device locatedbetween the traction unit 12 and the storage drum 16.

To achieve maximum load control, the traction unit 12 should be able toaccelerate as rapidly as possible. The inertia of the rotatingcomponents of the traction unit 12 can be kept low enough so that, withreasonable motor torque, high acceleration can be achieved. The storagedrum 16, however, has an inherent inertia at least 10 times that of thetraction unit 12. In order for the drum 16 to accelerate with thecapstan 24, a proportionately greater torque would be required. Theamount needed cannot reasonably be provided within the range of thedesign parameters of this winch l0, consequently paying cable in and outwould result in slacking and overtensioning the cable 22 between thetraction unit 12 and the drum 16. It is therefore necessary to eitherdecrease the acceleration of the traction unit 12 to whatever the drum16 can manage, or to put a buffer between the units. The cableaccumulator 14 serves as the buffer.

The cable accumulator 14, shown in greater detail in FIG. 2, isconceptually simple. It takes in or pays out cable to the traction unit12 or the storage drum 16 at a nearly constant tension. The rate andamount of cable 22 handled from either side are controlledindependently.

During operation, as the traction unit 12 accelerates to pay out cable,cable initially comes from the cable accumulator 14. As the accumulator14 is emptied, the storage drum l6 begins feeding cable in. The storagedrum l6 eventually reaches the speed or position required to hold theaccumulator 14 half full. For hauling in cable, the operation isanalogous. Thus, with the cable accumulator 14 to act as a buffer, thewinch system 10 can include a large, heavy, drum load of cable, whilemaintaining a high acceleration capability at the traction unit 12.

The storage drum 16 consists ofa flanged drum which can store 10,000feet of 'r-inch cable, and is driven through a gear reduction box by a50 hp. hydraulic motor with proportional torque control. A Lebusspooling system and a fleet-angle compensator are used on the storagedrum.

The hydraulic power supply 18 is the source of all oil used by thetraction unit 12 and the storage drum 16. It contains an oil reservoir,pumps, and heat exchanger required for this system.

The control console 20 provides complete remote control and monitoringof the winch system 10, by means of the signal carrying cable 19 (FIG.1). A monitor panel gives all pressures, torques, rates, and linetension, as well as load depth and attitude.

Discussing now FIG. 2 in more detail, the winch may be considered aconstant-tension winch, that is, its output is meant to have a constanttension. The cable accumulator 14 is a device which takes in or pays outcable, from either side, at a nearly constant tension. The cableaccumulator 14, which is situated between the storage drum 16 and thetraction unit 12, and operates to control the cable tension in thatregion, but it does not affect the tension of the cable 22 as the cableis payed out to the load. In the model shown in FIG. 2, the two sheaves26 and 28 at the bottom are fixed and the top sheave 30 can move up anddown. The top sheave 30 is supported on a hydraulic piston 32, moving ina vertical direction in a cylinder 33, which exerts an upward force, F.If the weight of the top sheave 30 and its support is W, then the cabletension 15 T=(FW)/2 l when the system is at rest. As the top sheave 30moves up 1 foot, it will pull in 2 feet of cable 22, from either or bothsides. As the sheave 30 comes down 1 foot, it lets 2 feet of cablereturn. Thus, if the tension in the cable 22 increases above T, cable istaken from the accumulator 14; if the tension drops below T, theaccumulator will take cable in.

The accumulator 14 actually used in the winch 10 is simply a row of nineof the simple three-sheave models 14, shown in FIGS. 1 and 2, placedside-by-side. The top block of sheaves, similar to sheave 30, has atotal travel of 5 feet, so the dynamic cable capacity of the unit isfeet.

It is important to note that no accumulator 14 of this type can maintaina constant tension in the cable 22, due to the mass and the inertia ofthe movable components. If the top sheave 30 and support have mass M andsheave moment ofindue to the vertical acceleration, where T and T arethe tensions defined in FIG. 2, and

where R is the sheave radius, to accelerate the sheave in rotation. T,is added to T in Eqs. (2) and (3) because in this case the top sheave 30is moving vertically, and both ends of the cable 22 at reference symbolsT and T representing tensions, are simultaneously being let out orpulled in. Tension T is sub tracted from tension T, in Eqs. (4) and (5)because the sheave 30 is rotated, and tension T is opposed to tension TIn units operating at high acceleration, these tension error terms canamount to hundreds of pounds. An additional tension error will exist asa function of top sheave 30 position, if the pressure in the hydrauliccylinder 32 is not kept constant. In a unit actually built, thispressure is held quite accurately by the scheme shown in FIG. 2.

In the fluid accumulator 34, the oil pressure in the fluid cylinder 36is balanced by the nitrogen pressure in the cylinder and in the nitrogenstorage bottles 38. As the piston 32 travels from top to bottom in thehydraulic cylinder, the amount of oil (or nitrogen) displaced is smallcompared to the total volume under pressure, hence the pressure changeis small.

Discussing now in detail the mode of winch operation wherein it isdesired to maintain the load 23 at a constant depth below the mean seasurface, in the course of taking data from instrument packages suspendedin the ocean, it is often desirable to cancel out the motion of the shipor vessel on the surface so that the load 23 remains relatively still,with respect to a vertical direction.

Control of the winch in this constant-depth mode is conceptually quitestraightforward. In order to hold the load 23 at a constant depth, thewinch 10 must pay out cable 22 as the vessel rises on a wave, then takecable in as the ship falls, with the amount and rate of cable motionjust compensating for ships motion.

Referring back to FIG. 1, the constant depth operation is as follows:The traction unit 12 is under control of the depth sensor, or sensorpackage, 21 through the control console 20. The depth sensor 211 isattached firmly to the winch cable 22 at a depth of approximately 300feet. This depth is great enough so that surface waves cannot cause asignificant error in the depth sensor output, yet shallow enough so thatthe mechanical delay down the winch cable 22 will not disrupt systemstability. The depth transducer, which is part of the sensor package 21,is capable of resolving a change in its depth to within less than 1 inchin 300 feet.

As the ship rises on a wave, the depth sensor will be pulled up by thecable 22. This produces an error signal which causes the traction unit22 to pay out cable 22 in order to return the sensor to its nominaldepth. As the ship comes down, the sensor package 211 will drop, causingthe traction unit 12 to take in cable 22, again returning the sensor toits nominal depth. Holding the depth sensor at a constant depth relativeto the mean ocean surface will maintain the load 23 at a relativelyconstant depth. The system is designed to operate under conditions of upto at least sea state 6 (wave heights to 30 feet) with sensor motionattenuated from the ships motion by a factor greater than H00.

During the constant-depth mode, the storage drum 16 is controlled by thecable accumulator M. The storage drum 16 is not ordered to turn unlessthe cable accumulator 14 is nearly full or nearly empty. This means thatas the traction unit 12 pays cable 22 in and out, compensating for theships motion, cable is taken from and stored in the cable accumulator l4and the drum 11h remains still.

Referring now to H6. 3, this figure shows a winch control system d0, foroperating a winch stationed on a vessel, and for stabilizing a load 23which is connected by a cable 22 to a traction unit 12 (FIG. 1) drivenby a prime mover (not shown), at a constant depth below the mean seasurface irrespective of the vertical motion of the vessel due to waveaction. The winch control system 40 includes, as a key element, a cabledynamics sensor 32, a component of the sensor package 211, connectableto the cable 22 between the traction unit 112 and the load 23 forgenerating output signals proportional (l) to its depth, and (2) to itsvelocity relative to the vessel. The cable dynamics sensor 42 containsan accelerometer and an integratorwithin it, and is therefore able tosense velocity. it also contains a pressure gauge, and is therefore ableto measure depth.

A tachometer, dd, connectable to the traction unit 12, has the purposeof producing a signal which is proportional to the velocity of the cable22 relative to the vessel. A depthwelocity summing circuit Ml, connectedto the cable dynamics sensor d2, is adapted to be connected to a sensordepth order signal MD, generated by the control console on the vessel,for summing the sensor depth 42D and the depth order signals, andconnected to the cable dynamics sensor and tachometer dd for summing thesenor velocity signal 42V and the cable velocity signal MV, and thensumming the two depth and the two velocity signals to produce an outputcontrol signal 46. A torque control W is connected from the output d6 ofthe depth-velocity summing circuit 50 to the prime mover 49, fordeveloping a torque signal proportional to the control signal, to causethe traction unit 112 to null the control signal, thereby controllingthe load position and velocity.

In the winch control system 40 of FIG. 3, the depth-velocity summingcircuit 50 consists of the following three summers:

a. a depth summer 52 for generating a depth error signal;

b. a velocity summer 54 for generating a velocity error signal; and

c. a depth-velocity summer 56, having as its two inputs the depth andvelocity output error signals, and generating the output control signal46.

The depth velocity summing circuit 50 would be on board the vessel andconnected by the cable 19 (FIG. 1) to the sensor package 21.

Discussing now quantitatively the signals of the servo loops shown inFIG. 3, the cable dynamics sensor 42 generates a signal 42D in A ma. perfoot corresponding to the depth at which it is located, for example 300feet, which depth may be measured by a-hydrostat, an element of thecable dynamics sensor 42.

The sensor depth order is a signal communicated from the control console20. It is chosen to also generate an output signal in Ama. per foot, andis a function of the difference between the actual depth at which it islocated and the desired depth for its location.

An example of the function of the sensor depth signal 42D and the depthorder signal 43D is the following: Assume that when the cable dynamicssensor 42 is at 300 feet, it generates a sensor depth signal current 42Dof +10 ma. The depth order signal 43D generated by the control console20 on the vessel will, providing that the desired depth for the cabledynamics sensor 42 is 300 feet, also be a signal current of i0 ma., butof the opposite sign, or direction. These two signals of the samemagnitude but of opposite polarity are summed together in the depthsummer 52, with a net sensor depth output signal 52D of 0 ma.

Now, if the cable dynamics sensor 42 should drop below its desired depthof 300 feet, by, say 5 feet, it will generate a sensor depth signal 42Dof, say, 50 ma., which would make the constant A equal to 10. Since thedepth order signal 43D generated by the console 20 is constant duringany single operation, the output signal, the sensor depth error signal52D, generated by the depth summer 52, will now be equal to 40 ma. Ineffect, the depth summer 52 cancels out the average value, +10 ma. inthis instance, and generates a depth output signal 52D equal to theerror signal.

Assuming that the cable dynamics sensor 42 is not in motion at thistime, both velocity inputs 42V and 44V to the velocity summer 54 areequal to zero, making the net output velocity error 54V equal to zero.Therefore, the only input signal to the depth-velocity summer 56 is the40 ma. error signal due to the cable dynamics sensor 42 being 5 feetlower than it should be. Hence, the output control signal 46 to thetorque control 48 would be of such a nature that it would cause thecapstan to exert sufiicient torque to rotate by a certain anglesufficient to lift the cable dynamics sensor 42, and therefore the load23, by 5 feet. That is, cable 22 is hauled upwardly, since the load 23was too deep.

The winch control system 40 for maintaining a load 23 at a constantdepth below the mean sea surface may also compensate for theacceleration of the load and reduce the error in the acceleration tozero. However, due to noise problems, it was found that avelocity-error, rather than acceleration-error, system was much easierto implement. The acceleration of the cable 22 wound around the pair ofcapstans 24 was therefore integrated once to result in a velocity signal44V relative to the ship.

The cable dynamics sensor 42, in addition to a hydrostat for measuringpressure, also contains an accelerometer to measure the verticalacceleration of the load 23. This acceleration is integrated once toproduce a sensor velocity signal 42V.

It should be noted that the sensor velocity signal 42V produced by thecable dynamics sensor 42 is relative to the means surface of the water,while the cable velocity signal 44V is relative to the vessel.

It is also tobe noted that the output control signal 46 is an errorsignal, say, of 40 ma., which may be due to an error in depth only, anerror in velocity only, or some combination of the two. In a manner ofspeaking, the torque control unit 48 sees" an error signal current of 40ma., but does not know its composition. Nevertheless, such systemsutilizing both position and rate feedback work quite well.

As the load 23 is hauled up for any reason, there is caused a cableacceleration with respect to the ship, which is integrated to produce arate signal 44V which is fed to the velocity summer 54. The movement ofthe load 23 upward also produces a rate signal 42V. Both rate signals42V and 44V are fed to the velocity summer 54, thus producing a netoutput velocity signal 54V, which gets smaller and smaller as the load23 approaches its desired position. The rate feedback due to bothsources stabilizes the circuit 49.

The whole loop response gives the result that, as the cable dynamicssensor 42 comes back to its nominal position of 300 feet, in the examplegiven, the depth error sum 52D approaches zero, and both rate terms 42Vand 44V will gradually decrease to zero. The load 23 approaches itsnominal position, as determined by the sensor depth order signal 43D, ina damped manner.

While there is a time delay between the instant of time when the sensorpackage 21 starts to move in a vertical direction and the time when thecable 22 is released or taken in, it should be noted that, as is typicalof servosystems of this type, the electrical and mechanical componentsare connected together in a common feedback system, and the delays areaccounted for in the design of the overall system.

An electrical signal may be sent to a mechanical component faster thanthe speed with which the component may respond, but because the reactionof the electrical components in the feedback loop are tied to thereaction of the mechanical components, they all work together withacceptable delays.

Summarizing the function of the depth-velocity summing circuit 50, itdetermines the error in two depth input signals 42D and 43D, and theerror in two velocity input signals, 42V and 44V and sums the twoerrors, in depth and velocity, to produce an output control error signal46 which applies a torque to the traction unit 12, to result in acapstan 24 rotation C E 10 ma./ft. Sensor position feedback D E 10maJft. Depth order term 430 from console (not a term in the aboveequation (6) G= G(s) is defined by equation (9), below k feedback gainoftorque control (K E lOuamp./ft.lb.)

This equation (6) does not describe the motion of the cable dynamicssensor 42, but rather the degree with which the sensor motion isdiminished relative to the ship's motion. Equation (6) for L(s) measuresthe attenuation for the ships motion in terms of the capstan 12 motion,just as though the system 40 were a single loop.

Discussing now FIG. 4, this figure shows the torque control 48 toconsist of a stroke cylinder 62 controlled by a servo valve 64, with afeedback transformer 66 feeding the output back into the input through afeedback transformer 66. The output control signal 46 goes to the torquecontrol unit 48, which controls a prime mover 49, which, in oneembodiment was a hydraulic motor 49A. The denominator of the transferfunction of the servo valve 64 is written in the standard form for asecond degree servo function.

The loop effectively gives a torque out of the motor 49A as a linearfunction of the drive signal, the output control signal 46. Theclosed-loop response ofthe control circuit 60 is out O O where o,,=o, c

w is the natural frequency of the servo valve 64, approximately 60c.p.s. in one embodiment.

G Servo valve gain (GPM/ma.)

G Stroke cylinder gain (FPS/6PM) G Hydraulic motor gain (Ft.-Lb./Ft.)

The open-loop form of the equation describing the ratio of load-motionto ship-motion (assuming stiff cable) is to 1 ML [1+KG(S)+{ G(8)AS M MomR M R mR G( J -l- J82 P) and angular velocity which tends to reduce thetwo errors to Where zero. The error output signal 46, in terms of theLaplace trans- G z forrn,isofthe form (k,+! .s). 50 G(S)=m (10) Inasmuchas the three summing circuits, the depth summer 52, the velocity summer54, and the depth-velocity summer 56 are all linear circuits, they couldbe combined into one circuit, the depth-velocity summing circuit 56), asshown in FIG. 3 by the dashed lines, with four inputs, 42D, 43D, 42V,and 44V and one output signal 46.

The Laplace transform for the overall circuit shown in FIG. 3 involves afifth-order term in s. However, the overall transfer function may besimplified to the following second-degree equation:

m mass of the load and cable in the water. 40 m I00 slugs in thisapplication, depending on th amount of cable reeled out.

R radius of capstans carrying the cable 12 inches) J 25 slug-ft. Momentof inertia of all rotating components, reflected to motor shaft sideofgearbox 51 (FIG. 5) M I00 ft.-lb./ma. Torque response of motor 49A toerror signal, and is further defined in connection with equation (8) A10 ma./ft./sec. =Capstan velocity 44V feedback term B 8 ma./ft./sec.Sensor velocity 42V feedback term C(s) is the transfer function of theforward-loop of the servovalve 64 and the hydraulic stroke cylindercontrolling torque on the capstan hydraulic motor 49A, with K being thefeedback gain offeedback amplifier 66 on this minor loop 60.

Referring now to FIG. 5, this figure shows, in block diagram form, awinch control system wherein the prime mover may further comprise thehydraulic motor 49A with proportional torque control 48, as shown in theprevious figure, controlled by the output of the torque control; and inaddition may comprise a gear reduction box 51, driven by the hydraulicmotor, whose output is connected to the capstans 24.

Also shown in FIG. 5, as an optional part of the winch system, is acable-tension monitoring system 71 which includes a load cell 72 whichmakes contact with and senses the tension in the cable 22. A high-lowthreshold device 74, connected to the load cell 72, senses when thecable tension is not with a desired range. A braking device 76,connected to the cable 22 (not shown) and controlled by the high-lowthreshold device 74, brakes the cable when the tension is too low or toohigh.

In conclusion, operation of the hydrographic winch having features ofthis invention has demonstrated that a generally useful, highspeed,high-power winch can be built which is capable of:

a high line rates and acceleration, provided by the large drive andinherently low inertia of the traction unit 12,

b. complete control of the cable 22 in the system, provided by the cableaccumulator l4 acting as a buffer between the traction unit [2 andstorage drum [6, and cable tension feedback into the control system fromthe load side; and

c. reduced transient power loads on the ship's electrical system,through use of the energy storage capability of the hydraulic system.

In addition, the winch is equipped with controls to automaticallycompensate for ships motion with cable motion, so that the suspendedload 23 will remain nearly stationary with the respect to the mean seasurface.

d. the use of variable displacement hydraulic motors 49A operating froma pressure source 34 makes energy storage and dissipation easy, andoffers the most flexible, controllable system for this application; and

e. the position-order control system, with maximum rate control, givesthe operator the closest control of the load 23 under all conditions.

We claim:

1. A winch control system, for controlling a winch stationed on avessel, used for stabilizing a load, which is connectable by a cable toa traction unit driven by a prime mover, at a constant depth below themeans surface of the sea irrespective of the vertical motion of thevessel due to wave action, comprismg:

a cable dynamics sensor connectable to the cable between the tractionunit and the load, for generating two output signals, one signal beingproportional to the depth of the sensor and the other signal beingproportional to the velocity of the sensor relative to the vessel;

a tachometer, connectable to the traction unit, for producing a signalwhich is proportional to the velocity of the cable relative to thevessel;

a depth-velocity summing circuit connected to the cable dynamics sensorand adapted to be connected to a sensor depth order signal generated bya control console on the vessel, for summing the sensor depth and depthorder signals, and connected to the cable dynamics sensor and tachometerfor summing the sensor velocity and cable velocity signals, and thensumming the two depth and velocity signals to produce an output controlsignal; and

a torque control adapted to be connected from the output of thedepth-velocity summing circuit to the prime mover,

for developing a torque signal proportional to the control signal, tocause the traction unit to null the control signal,

thereby controlling the load position and velocity.

2. A winch control system according to claim 1, wherein thedepthvelocity summing circuit consists of three summers:

l. a depth summer, whose two inputs are the depth order signal and thesensor depth signal, for generating an output depth error signal;

2. a velocity summer, whose two inputs are the signal from thetachometer and the sensor velocity signal, for generating an outputvelocity error signal; and

3. a depth-velocity summer, having as its two inputs the depth andvelocity output error signals, for generating the output control signal.

3. A winch control system according to claim 2, further comprising thefollowing elements mounted on the vessel:

a cable tension monitoring system which includes a load cell which makescontact with and senses the tension in the cable;

a high-low threshold device, connected to the load cell, which senseswhen the cable tension is not within a desired range; and

a braking device, connected to the cable and connected to and controlledby the high-low threshold device, which brakes the cable when thetension is too low or when the tension is too high, to avoid slack cableand/or broken cable.

4. A winch control system according to claim 2, further comprising:

the traction unit, mounted on the vessel.

5. A winch control system according to claim 4, wherein the tractionunit further comprises:

a pair of ca stans grooved for accepting the cable.

6. A wine control system according to claim 5, further comprising:

the prime mover, l on the vessel.

7. A winch control system according to claim 6, wherein the prime moverfurther comprises the following elements mounted on the vessel:

a hydraulic motor with proportional torque control, connected to andcontrolled by the output of the torque control; and

a gear reduction box, connected to and driven by the hydraulic motor,whose output is connected to capstans.

1. A winch control system, for controlling a winch stationed on avessel, used for stabilizing a load, which is connectable by a cable toa traction unit driven by a prime mover, at a constant depth below themeans surface of the sea irrespective of the vertical motion of thevessel due to wave action, comprising: a cable dynamics sensorconnectable to the cable between the traction unit and the load, forgenerating two output signals, one signal being proportional to thedepth of the sensor and the other signal being proportional to thevelocity of the sensor relative to the vessel; a tachometer, connectableto the traction unit, for producing a signal which is proportional tothe velocity of the cable relative to the vessel; a depth-velocitysumming circuit connected to the cable dynamics sensor and adapted to beconnected to a sensor depth order signal generated by a control consoleon the vessel, for summing the sensor depth and depth order signals, andconnected to the cable dynamics sensor and tachometer for summing thesensor velocity and cable velocity signals, and then summing the twodepth and velocity signals to produce an output control signal; and atorque control adapted to be connected from the output of thedepth-velocity summing circuit to the prime mover, for developing atorque signal proportional to the control signal, to cause the tractionunit to null the control signal, thereby controlling the load positionand velocity.
 2. A winch control system according to claim 1, whereinthe depth-velocity summing circuit consists of three summers:
 2. avelocity summer, whose two inputs are the signal from the tachometer andthe sensor velocity signal, for generating an output velocity errorsignal; and
 3. A winch control system according to claim 2, furthercomprising the following elements mounted on the vessel: a cable tensionmonitoring system which includes a load cell which makes contact withand senses the tension in the cable; a high-low threshold device,connected to the load cell, which senses when the cable tension is notwithin a desired range; and a braking device, connected to the cable andconnected to and controlled by the high-low threshold device, whichbrakes the cable when the tension is too low or when the tension is toohigh, to avoid slack cable and/or broken cable.
 3. a depth-velocitysummer, having as its two inputs the depth and velocity output errorsignals, for generating the output control signal.
 4. A winch controlsystem according to claim 2, further comprising: the traction unit,mounted on the vessel.
 5. A winch control system according to claim 4,wherein the traction unit further comprises: a pair of capstans groovedfor accepting the cable.
 6. A winch control system according to claim 5,further comprising: the prime mover, 1 on the vessel.
 7. A winch controlsystem according to claim 6, wherein the prime mover further comprisesthe following elements mounted on the vessel: a hydraulic motor withproportional torque control, connected to and controlled by the outputof the torque control; and a gear reduction box, connected to and drivenby the hydraulic motor, whose output is connected to capstans.